Actor Sean Penn rides shotgun through the flooded streets of New Orleans – but the anti-war activist insists the gun isn’t his.

Penn made headlines this week when he was seen helping stranded victims of Hurricane Katrina find safety from the fetid floodwaters that submerged the Crescent City.

But on Tuesday, Hollywood liberal looked more like Charlton Heston, prowling the storm-ravaged remains of the Big Easy loaded for bear.

A shutterbug snapped him after he got out of a boat in the city’s stately Garden District with a pump-action shotgun in his right hand and a flak jacket in his left.

It was unknown whether the shotgun was loaded.

Penn spokeswoman Mara Buxbaum said the weapon is not Penn’s.

She said that she did not know exactly how Penn suddenly became a poster child for the Second Amendment, but that the gun somehow wound up in his possession in the midst of the city’s chaos.

“It was in the boat, and he picked it up and carried it,” Buxbaum said. “It was in the midst of helping three or four people who were being rescued, whom he brought to the hospital.”

When asked by photographer Edward Keating what he was doing, Penn only said, “I care about the people, and I care about this city, and I want to help.”

Asked if Penn fired the gun – or shot anyone – Buxbaum said “never.”

Buxbaum said the gun was eventually “placed safely” with someone and that Penn, who has left the city, no longer had it.

Keating said he was surprised when he first saw someone holding a shotgun in the Garden District, because it was unusual to see an armed civilian in the street in broad daylight by that point in the unfolding tragedy.

The lensman said he was doubly surprised when he approached and saw that the man with the gun was Penn.

“I was like ‘Oh, Jesus, wow,'” he said.

Keating said he did not know what Penn did with the gun. Minutes later, Keating saw Penn doing an interview with a TV crew without the weapon.

This isn’t the first firearm folly for Penn.

During his 1985 wedding to Madonna, he allegedly fired a gun at paparazzi trying to photograph the nuptials from a helicopter.

The actor later drew criticism in 2003 when it was reported he had obtained a permit to carry a concealed weapons because of threats from a disgruntled employee – and that two of the guns he was permitted to carry were stolen along with his car.

One of the guns was later found at the home of a shooting suspect. It is not believed the weapons were used in any crime.